In today's mobile telecommunication networks, the operator of a mobile network is able to maintain tight control over the calls made and services used by its subscribers when they are at home, i.e. when they are registered with the operator's own network. For example, if a subscriber exceeds his calling credit limit the operator can notify the subscriber of this situation and/or can prevent the subscriber from making further calls until his outstanding account is settled. Similarly, where a subscriber makes use of a top-up account, e.g. using scratch cards to credit his account, an operator can restrict the subscriber's access when the subscriber's credit drops to zero. Such charging control is possible because of the introduction into mobile networks of Intelligent Network (IN) nodes which use the so-called Intelligent Network Application Part (INAP) protocol to communicate with one another. Problems arise however when a mobile subscriber roams outside of his home network and registers with a foreign network. Charging mechanisms currently in use for roaming subscribers are slow and cumbersome, resulting in the barring of roaming services to certain classes of subscriber (e.g. pre-paid subscribers). Furthermore, whether a subscriber is at home or roaming “abroad”, current charging mechanisms do not lend themselves to flexible charging schemes such as are desired by network operators.
In order to overcome the problems of existing charging mechanisms, a mechanism referred to as Customised Applications for Mobile network Enhanced Logic (CAMEL) has been standardised by ETSI (further enhancements to CAMEL are in the process of being standardised according to CAMEL phase 2 and phase 4). CAMEL provides for the transfer of charging related information in real time between a Service Control function (SCF) associated with a Cost Control Function (CCF) (the CCF is usually running at a Cost Control Node (CCN) located in a subscriber's home network) and a Service Switching Function (SSF) typically running at, or associated with, an MSC or GMSC (in the case of a GSM network) with which a subscriber to be charged is registered. The SSF may be located in the same network as the SCF or in a different network.
A feature of CAMEL is that it allows charging elements to be sent from an SCF/CCN to a SSF prior to and during a call involving a mobile terminal registered with an MSC/GMSC. A charging element defines a tariff for a call or part of a call or for some other service (e.g. data transfer), and may be used to calculate a charge. The charging element may be sent to a subscriber's terminal, e.g. according to the Advice Of Charge (AoC) service, by the SSF.